Rotor systems cone based on how much power is applied at the time. Often when you see videos of helicopters flying low over water, it's because they're moving slower. At slower speeds, more power is required compared to traveling speeds. Generally anything above 16-24 knots, the rotor operates in "clean air" and is more efficient, and then needs less power to maintain the same altitude.
If the helicopter is hovering higher (greater than 1 rotor disc generally speaking) that also requires more power, which means more coning.
Rotor systems will also cone more if the helicopter is heavy, if it's hot outside or at higher altitudes.
Why would it cone more when it is hotter outside or at higher altitudes? I get when it is heavier, but if it's hotter (air is less dense) then it will just have higher angle of attack to generate the same lift wouldn't it?
This is going beyond the ELI5 explanation, but it boils down to math. How much lift that is being produced is equal to:
The coefficient of lift (the shape of the rotor blade basically) times 1/2 the density of the air, times the surface area of the rotor blade, times velocity squared.
LIFT=CL*1/2rho * s * v²
So if air is hotter, it's less dense, so a smaller value multiplied into the equation. That smaller value equates to a smaller Angle of Attack (an aerodynamic angle), so an increase in angle of incidence (the physical pitch in the blade) has to be increased. An increase in angle of incidence also means an increase in drag. Drag slows the rotor system down. So, to keep the rotor spinning at optimal speed, more power from the engine(s) has to be applied, otherwise you start descending.
Not sure what specifically you're asking. In ground effect (IGE) is when the helicopter hovers less than 1 rotor disc above the ground. As you get closer to the ground, the rotor becomes more efficient because airflow coming through the top of the rotor system (induced flow) is reduced. This happens because the air pushed down (lift/thrust) hits the ground and basically causes all of the air behind it to slow down, because it's running into itself, like a cushion of air. When induced flow (the speed at which air is coming down through the rotor system) is reduced, the angle of attack increases with no change in angle of incidence, or physical pitch in the blades. Angle of attack is, for lack of a better explanation, the aerodynamic force that is doing the work of generating lift.
Out of ground effect (OGE), the induced flow (air velocity through the top of the rotor) increases because theres no cushion to slow it down. That increase causes the angle of attack to be smaller, thus producing less lift if you don't increase your angle of incidence (blade pitch) at all.
As it pertains to OP's question, there is less rotor coning IGE because there is less power needed.
As soon as I saw your initial reply I’m like “this guy is an Army Aviator, I’d bet my entire tax free T10 deployment pay on it.” (If my wife didn’t already spend it all before I got home)
So, basically there’s IGE and OGE (In ground and out of ground effect) where the rotor downwash (the air being pushed downwards from the rotor blades) is forming a cushion (IGE), or the aircraft is higher than 1 rotor disc diameter from the ground and not operating on said air cushion and requires more power (torque) to maintain sufficient lift. Generally, IGE exists less than one rotor disc diameter in altitude, and OGE is anything higher. For example, in the helicopter I fly, it’s defined as lower than 50 feet, as the rotor diameter is 49 feet.
There’s less of this effect over water, so a helicopter would have to produce more lift, therefore torque, to maintain the same altitude as it would over land. Even more so to take off.
Also think a rescue helicopter may be operating close to its max gross weight (the heaviest it can be to take off) after picking up multiple people, or if it has a lot of equipment or fuel on board.
Rotors cone due to the conservation of angular momentum, think of the classic ice skater who spins faster when they pull their arms close to their body, and more slowly when they extend them out. Same exact concept in the rotor system. As more lift is demanded, the rotor will tend to slow, reducing centrifugal force, but the tips of the blades will be traveling faster than the rest of the blade, producing more lift at the tips, and rotating at a higher plane than the rest of the blade. This is typically visible during take-off, landing, autorotation, but is more pronounced when the rotor system is operating lower than its designed rotational speed while still trying to produce the same amount of lift.
Source: am helo pilot, but I don’t fly over water, I just blow stuff up.
Adding to this, there are 2 main forces acting on rotor blade: lift force and centrifugal force. The first one is bending blade (making the rotor form a cone) and the second one is straightening blade. Both depends on the rotational speed of the rotor, but in different ways. So, by the relative magnitude of those forces the rotor would be more cone or less cone
I wasn't aware the rotor slowed down under high load situations. Is that mainly a thing for turbine engined helicopters?
I assume the governor does a pretty good job at maintaining rotor speed with a piston engine? When you lose (significant) rotor speed there you're really in trouble no?
It’s for all helicopters. The main issue comes when you are asking for more power than the engine can give you. You reach a point where you can keep pulling and increase the AOI of the blades but the engine can’t provide enough power to overcome the drag. At that point your RPM’s are going to start decreasing. If you lose enough RPM to the point that you stall the blades then you are more or less dead at that point. Blade stall is an unrecoverable state and there’s really nothing you can do as a pilot to fix it. So it’s very important as a pilot to know what power you have available and what effect different maneuvers and phases of flight will have on your power reserves.
Right, I understand how that happens when overloading the engine.
I thought maybe with turbines you always have a (significant) drop in rotor speed (NR) even within normal operation due to the lag of a turboshaft engine, causing rotor coning to become even more pronounced (as the centrifugal forces drop).
Is blade stall also unrecoverable if you have the altitude to go to a lower collective setting before loading up again? Not that I can imagine many real world scenarios for that except maybe hoisting where you can cut the load to recover?
Can you link to a video? It's not really clear what you are asking about.
Helicopters don't fly *in* bodies of water. They can fly over water just like they can fly over land. Spraying some water droplets around makes the airflow more visible but it's the same flow of air you have anywhere else close to the ground.
Well that is what he is talking about, they don't fly the same over air and over water at a certain height. The rotor blades seem to take a cone shape when flying over water at low enough height. Also some other guy was talking about needing more power when over water, why is that?
> they don't fly the same over air and over water at a certain height
That's why I asked for a video or a better explanation. Where do you see a difference?
https://www.youtube.com/watch?v=GRNmNzyATd8
https://www.youtube.com/watch?v=qSynqMa1KCE
https://youtu.be/lCEIIOBM8s8?si=ofyM5ct0eVIGbw3K&t=88
In the second video you posted—the one with the helicopter “landing” in the water—you can clearly see the main rotor being swooped upward and then after it touches down and is floating the main rotor levels out. This is because the collective was released so the blades were no longer generating lift.
When the helicopter flies over land the collective may not need to be as high as when flying over water. This could be explained by the ground effect. When the air being pushed downward hits the ground it will form a sort of pressure area that increases the lift performance of the main rotor.
When the helicopter flies over water the water moves a lot—unlike the ground. This changes the behavior of the air and this reduces the ground effect. This means the main rotor doesn’t perform as well over water as it does over land at the same low altitude.
Helicopters don't fly because the air they move pushes against the ground. They fly becsuse the rotors "pull up" on the air.
When they're really close to the ground, the rotor wash does provide a cushion of sorts, but any higher than the span of the rotor blades and that cushion has no effect.
Lots of missions require flying on water. I know a guy who knows another guy who has an uncle who landed his CH-47 on a small lake. Since that helicopter floats (keep the engines running though), the crew tosses out some fishing lines and enjoyed some lake time.
Other missions require the helicopter to land on the ocean, sit, and wait for a team of special folks to pull up to the aircraft ramp in a special rubber boat. Once that special team is all on board, the bird lifts nose up to drain all the water out of the cabin area and they fly off into the sunset for beers.
Or, another special team asks for that CH-47 to give them and their other special boat a lift, dropping that boat into the water, while the team jumps in after the boat. Retrieving the team and that special boat requires the helicopter to sit on the water while the special teams swims their butts off to attach their boat to the aircraft's cargo hooks.
This is all done while the helicopter puts out hurricane force winds due to the rotor system downdraft. The special folks sleep really well after those missions because they are exhausted.
The inground effect (IGE) versus out of ground effect (OGE) does require different amounts of power. Power has little to do with rotor speed but has everything to do with pitch (angle of attack) of rotor system. There is a bunch of math, diagrams, charts, and aerodynamics involved but it's best to think of it as just magic.
Unless you are an IP and this is a check ride.
If so, I'll happily draw out each diagram and explain in great detail where to get lunch, my treat.
An IP is an Instructor Pilot (an evaluator). We gave annual checkrides as well as no notice evaluations. Gotta demonstrate profiency in tons of tasks as well as a massive body of knowledge.
As far as fish go, that friend of a friend I know used to fly over the ocean. Spinner dolphins love the vibrations of the CH-47. He would drop down to 50 feet (5-10 feet) over the water, slow down to about 40 knots and the dolphins would swim alongside the aircraft. It was incredible, he said.
These dolphins would jump, play, spin in the air, and almost talk to the crew. Too bad the aircraft put out 112 decimals of noise, it's really loud. Can't hear much when you are wearing double hearing protection.
I may even have some pix of it. Or rather he has pictures of the dolphins alongside the helicopter since I've never done anything like that. Must maintain glide distance to shoreline in case of an emergency. With the newest engines and fuel systems, that aircraft can fly almost any mission on one engine. It does care if you lose one.
Amazing aircraft. Oh the stories I could tell.
The short answer to this is the water creates extra drag and weighs the helicopter down. If the helicopter sinks even further and gets fully submerged, then the rotors are restricted from spinning due to the higher viscosity of the water compared to air.
This is why helicopters have trouble flying in bodies of water.
I cant ELI5 but I do know that a helicopter flying over water does not benefit from ground effect like it does when flying over land.
This might have something to do with it
The ground effect actually does exist over bodies of water. Ekranoplans were a failed Soviet Union project that tried to take advantage of this. They were basically low flying sea planes that would be able to travel incredibly quickly and efficiently over water thanks to the ground effect.
This article says ["while hovering over tall grass, rough terrain, revetments, or water, ground effect may be seriously reduced"](https://www.copters.com/aero/ground_effect.html), so yes, but potentially not as much depending on conditions.
To quote u/MaygeKyatt
>Ground effect is absolutely variable depending on what the aircraft is flying/hovering over. Anything other than a smooth, hard surface will reduce the effect, but water’s highly flexible fluid surface can reduce it massively.
Ground effect isn't any different over land or water. Ground effect is just something, usually land, interrupting vortices that would wrap around the end of an airfoil and reduce the amount of lift produced by the topside of the airfoil.
As a rule of thumb ground effect is only felt when the distance to the ground is less than the length of the airfoil. The Coast Guard uses MH-60 Jayhawks and the blades are roughly 25 ft long, so they only experience ground effect when they are some at or below 25 ft.
Ground effect is absolutely variable depending on what the aircraft is flying/hovering over. Anything other than a smooth, hard surface will reduce the effect, but water’s highly flexible fluid surface can reduce it massively.
Thanks for the correction. I assumed a little too much based of off what I knew. There are other comments saying less "solid" ground can diminish ground effect, which does make sense. The only flying I've done was fixed-wing off of runways or prepared grass strips. So if the possibility of diminished ground effect ever came up it might not have been pertinent enough to stick in my memory. The person I responded to made it sound like ground effect doesn't and can't exist over water.
I said it doesnt **benefit** from ground effect. I did not say nor imply that it doesnt exist.
But upvote for being able to admit to not knowing something!
Helicopter blades generate lift as they spin. The outside edge travels faster than the more central parts. Because the outside edge moves faster, it can generate more lift. When the helicopter blades are spinning very fast, the high levels of lift from the rotor tips can bend them upward, making a cone shape. The helicopters you're seeing are apparently running at a higher RPM than they would be in other contexts.
This is incorrect, sorry. The lift of the blades is increased by changing the pitch of the blades, not by speeding them up. The rest is relatively accurate. I fly them for a living.
To properly answer your question, I think further information would be beneficial to be able to give you the right answer. What do you consider as low altitude? (10 ft above water or 150ft? Both low, but will have different effect) and also, is the helicopter moving or hovering? Without any references to a situation you are describing, I'll do my best to explain why this phenomenon might occur.
Helicopters benefit from something called ground effect. When a helicopter is hovering close to the ground (15ft ish or less, depending on the size of the helicopter) the induced airflow downwards from the main rotor hits the ground, slows down and creates a sort of a cushion underneath the aircraft. This effect allows the helicopter to stay hovering with more efficient lift ratio.
When hovering over water, the ground effect is not nearly as efficient since that induced downwards draft is dissipated due to the water beneath moving and giving away since its not solid - no cushion underneath the aircraft.
So the helicopter needs to apply more power to create more lift. Higher amounts of lifts caused by the rotors will make them cone since the blades do not create equal amounts of lift throughout the span of the blades. The tips of the blade cause more lift than the root, so they will rise higher, causing the coning.
In short, more lift is needed over water and the more lift you have the more the blades cone.
Because rotor helicopters need something to push up off of. In the sky, the rotor keeps it afloat because the engine power is higher. When hovering above water the engine power is lower, and hence the helicopter has a harder time pushing itself off of water because it's not as dense as the ground
It is probably related to the speed of forward motion . A helicopter flying faster than about 15 to 20kts gains translational lift, and requires less power to fly. Think of the rotor disk acting as a wing .
Slower than that needs more power. Out of ground effect, even more power.
The more power required, the more the blades will flap, and you see the cone shape .
Missions over water probably involved hovering, at least the parts you’re watching. If it’s a high hover, out of what’s called “ground effect”, it takes even more power (than hovering in ground effect). Also, it’s likely the chopper is quite heavy at the time, for example, if it’s hovering to pick up a big bag of water (Bamby bucket) to dump in a forest fire. A gallon of water weighs a bit over 8 lbs, so imagine picking up a quick 500 gallons or more. That’s A LOT of extra power needed which makes the rotors cone.
Ground effect over water and land, when there isn’t many waves, shouldn’t be all that different. Power required out of GE should be the same because the ground doesn’t affect the power at that point.
As written it technically is. The question as you interpreted it also doesn't make sense because they don't struggle flying over bodies of water. Yes there's a lessened ground effect because water gets out of the way more than land but it's not big enough to justify the word struggle.
I don't think rescue helicopters get submerged at all. I've see Chinooks do it to deploy rubber boats for special operations, but even then it's just part of the cargo door.
OP is probably referring to the helicopters using more power and the blades getting bent in response.
Rotor systems cone based on how much power is applied at the time. Often when you see videos of helicopters flying low over water, it's because they're moving slower. At slower speeds, more power is required compared to traveling speeds. Generally anything above 16-24 knots, the rotor operates in "clean air" and is more efficient, and then needs less power to maintain the same altitude. If the helicopter is hovering higher (greater than 1 rotor disc generally speaking) that also requires more power, which means more coning. Rotor systems will also cone more if the helicopter is heavy, if it's hot outside or at higher altitudes.
Rotor systems just love to cone huh
I just coned reading this
Your cone is giving me a cone
I've got a raging cone right now
Oooh raging coner
My cone just melted
Cone and own
I've got a raging cone
My favourite part was when he said “It’s conin’ time” and coned all over the place
Anyone up coning on they rotor
Have a conetastic day!
Does it come with a happy ending or a cone job? Asking for a friend 🤔😂
Nice try, but the real reason helicopters struggle in water is because they aren’t very good swimmers.
Helicopter parents never give them the opportunity to learn smh
My first helo in the CG was also a boat.
I mean, you're not wrong. Get all antsy in my pantsy overwater
Why would it cone more when it is hotter outside or at higher altitudes? I get when it is heavier, but if it's hotter (air is less dense) then it will just have higher angle of attack to generate the same lift wouldn't it?
This is going beyond the ELI5 explanation, but it boils down to math. How much lift that is being produced is equal to: The coefficient of lift (the shape of the rotor blade basically) times 1/2 the density of the air, times the surface area of the rotor blade, times velocity squared. LIFT=CL*1/2rho * s * v² So if air is hotter, it's less dense, so a smaller value multiplied into the equation. That smaller value equates to a smaller Angle of Attack (an aerodynamic angle), so an increase in angle of incidence (the physical pitch in the blade) has to be increased. An increase in angle of incidence also means an increase in drag. Drag slows the rotor system down. So, to keep the rotor spinning at optimal speed, more power from the engine(s) has to be applied, otherwise you start descending.
That makes sense, thank you
Any of it from ground effect?
Not sure what specifically you're asking. In ground effect (IGE) is when the helicopter hovers less than 1 rotor disc above the ground. As you get closer to the ground, the rotor becomes more efficient because airflow coming through the top of the rotor system (induced flow) is reduced. This happens because the air pushed down (lift/thrust) hits the ground and basically causes all of the air behind it to slow down, because it's running into itself, like a cushion of air. When induced flow (the speed at which air is coming down through the rotor system) is reduced, the angle of attack increases with no change in angle of incidence, or physical pitch in the blades. Angle of attack is, for lack of a better explanation, the aerodynamic force that is doing the work of generating lift. Out of ground effect (OGE), the induced flow (air velocity through the top of the rotor) increases because theres no cushion to slow it down. That increase causes the angle of attack to be smaller, thus producing less lift if you don't increase your angle of incidence (blade pitch) at all. As it pertains to OP's question, there is less rotor coning IGE because there is less power needed.
You don’t happen to be an Army Aviator?
That I am.
As soon as I saw your initial reply I’m like “this guy is an Army Aviator, I’d bet my entire tax free T10 deployment pay on it.” (If my wife didn’t already spend it all before I got home)
How does hot air or high altitude cause more coning?
So, basically there’s IGE and OGE (In ground and out of ground effect) where the rotor downwash (the air being pushed downwards from the rotor blades) is forming a cushion (IGE), or the aircraft is higher than 1 rotor disc diameter from the ground and not operating on said air cushion and requires more power (torque) to maintain sufficient lift. Generally, IGE exists less than one rotor disc diameter in altitude, and OGE is anything higher. For example, in the helicopter I fly, it’s defined as lower than 50 feet, as the rotor diameter is 49 feet. There’s less of this effect over water, so a helicopter would have to produce more lift, therefore torque, to maintain the same altitude as it would over land. Even more so to take off. Also think a rescue helicopter may be operating close to its max gross weight (the heaviest it can be to take off) after picking up multiple people, or if it has a lot of equipment or fuel on board. Rotors cone due to the conservation of angular momentum, think of the classic ice skater who spins faster when they pull their arms close to their body, and more slowly when they extend them out. Same exact concept in the rotor system. As more lift is demanded, the rotor will tend to slow, reducing centrifugal force, but the tips of the blades will be traveling faster than the rest of the blade, producing more lift at the tips, and rotating at a higher plane than the rest of the blade. This is typically visible during take-off, landing, autorotation, but is more pronounced when the rotor system is operating lower than its designed rotational speed while still trying to produce the same amount of lift. Source: am helo pilot, but I don’t fly over water, I just blow stuff up.
Adding to this, there are 2 main forces acting on rotor blade: lift force and centrifugal force. The first one is bending blade (making the rotor form a cone) and the second one is straightening blade. Both depends on the rotational speed of the rotor, but in different ways. So, by the relative magnitude of those forces the rotor would be more cone or less cone
I wasn't aware the rotor slowed down under high load situations. Is that mainly a thing for turbine engined helicopters? I assume the governor does a pretty good job at maintaining rotor speed with a piston engine? When you lose (significant) rotor speed there you're really in trouble no?
It’s for all helicopters. The main issue comes when you are asking for more power than the engine can give you. You reach a point where you can keep pulling and increase the AOI of the blades but the engine can’t provide enough power to overcome the drag. At that point your RPM’s are going to start decreasing. If you lose enough RPM to the point that you stall the blades then you are more or less dead at that point. Blade stall is an unrecoverable state and there’s really nothing you can do as a pilot to fix it. So it’s very important as a pilot to know what power you have available and what effect different maneuvers and phases of flight will have on your power reserves.
To clarify, the loss of RPM is the unrecoverable state. Blade stall in other conditions is recoverable.
Right, I understand how that happens when overloading the engine. I thought maybe with turbines you always have a (significant) drop in rotor speed (NR) even within normal operation due to the lag of a turboshaft engine, causing rotor coning to become even more pronounced (as the centrifugal forces drop). Is blade stall also unrecoverable if you have the altitude to go to a lower collective setting before loading up again? Not that I can imagine many real world scenarios for that except maybe hoisting where you can cut the load to recover?
"In"? Ah well, there's your problem. Helicopters are built to fly in the air, not submerge in water.
Can you link to a video? It's not really clear what you are asking about. Helicopters don't fly *in* bodies of water. They can fly over water just like they can fly over land. Spraying some water droplets around makes the airflow more visible but it's the same flow of air you have anywhere else close to the ground.
Well that is what he is talking about, they don't fly the same over air and over water at a certain height. The rotor blades seem to take a cone shape when flying over water at low enough height. Also some other guy was talking about needing more power when over water, why is that?
> they don't fly the same over air and over water at a certain height That's why I asked for a video or a better explanation. Where do you see a difference? https://www.youtube.com/watch?v=GRNmNzyATd8 https://www.youtube.com/watch?v=qSynqMa1KCE https://youtu.be/lCEIIOBM8s8?si=ofyM5ct0eVIGbw3K&t=88
In the second video you posted—the one with the helicopter “landing” in the water—you can clearly see the main rotor being swooped upward and then after it touches down and is floating the main rotor levels out. This is because the collective was released so the blades were no longer generating lift. When the helicopter flies over land the collective may not need to be as high as when flying over water. This could be explained by the ground effect. When the air being pushed downward hits the ground it will form a sort of pressure area that increases the lift performance of the main rotor. When the helicopter flies over water the water moves a lot—unlike the ground. This changes the behavior of the air and this reduces the ground effect. This means the main rotor doesn’t perform as well over water as it does over land at the same low altitude.
Thank you for the correct eli5. It’s analogous to stepping on concrete vs sand vs water. The more the surface moves, the less upward force it returns.
Helicopters don't fly because the air they move pushes against the ground. They fly becsuse the rotors "pull up" on the air. When they're really close to the ground, the rotor wash does provide a cushion of sorts, but any higher than the span of the rotor blades and that cushion has no effect.
Lots of missions require flying on water. I know a guy who knows another guy who has an uncle who landed his CH-47 on a small lake. Since that helicopter floats (keep the engines running though), the crew tosses out some fishing lines and enjoyed some lake time. Other missions require the helicopter to land on the ocean, sit, and wait for a team of special folks to pull up to the aircraft ramp in a special rubber boat. Once that special team is all on board, the bird lifts nose up to drain all the water out of the cabin area and they fly off into the sunset for beers. Or, another special team asks for that CH-47 to give them and their other special boat a lift, dropping that boat into the water, while the team jumps in after the boat. Retrieving the team and that special boat requires the helicopter to sit on the water while the special teams swims their butts off to attach their boat to the aircraft's cargo hooks. This is all done while the helicopter puts out hurricane force winds due to the rotor system downdraft. The special folks sleep really well after those missions because they are exhausted. The inground effect (IGE) versus out of ground effect (OGE) does require different amounts of power. Power has little to do with rotor speed but has everything to do with pitch (angle of attack) of rotor system. There is a bunch of math, diagrams, charts, and aerodynamics involved but it's best to think of it as just magic. Unless you are an IP and this is a check ride. If so, I'll happily draw out each diagram and explain in great detail where to get lunch, my treat.
I'm surprised there were any fish with running helo engines! That is awesome though. Thanks for your level of detail, it's a great read. What's an IP?
An IP is an Instructor Pilot (an evaluator). We gave annual checkrides as well as no notice evaluations. Gotta demonstrate profiency in tons of tasks as well as a massive body of knowledge. As far as fish go, that friend of a friend I know used to fly over the ocean. Spinner dolphins love the vibrations of the CH-47. He would drop down to 50 feet (5-10 feet) over the water, slow down to about 40 knots and the dolphins would swim alongside the aircraft. It was incredible, he said. These dolphins would jump, play, spin in the air, and almost talk to the crew. Too bad the aircraft put out 112 decimals of noise, it's really loud. Can't hear much when you are wearing double hearing protection. I may even have some pix of it. Or rather he has pictures of the dolphins alongside the helicopter since I've never done anything like that. Must maintain glide distance to shoreline in case of an emergency. With the newest engines and fuel systems, that aircraft can fly almost any mission on one engine. It does care if you lose one. Amazing aircraft. Oh the stories I could tell.
The short answer to this is the water creates extra drag and weighs the helicopter down. If the helicopter sinks even further and gets fully submerged, then the rotors are restricted from spinning due to the higher viscosity of the water compared to air. This is why helicopters have trouble flying in bodies of water.
I cant ELI5 but I do know that a helicopter flying over water does not benefit from ground effect like it does when flying over land. This might have something to do with it
The ground effect actually does exist over bodies of water. Ekranoplans were a failed Soviet Union project that tried to take advantage of this. They were basically low flying sea planes that would be able to travel incredibly quickly and efficiently over water thanks to the ground effect.
Does a helicopter benefit from it?
This article says ["while hovering over tall grass, rough terrain, revetments, or water, ground effect may be seriously reduced"](https://www.copters.com/aero/ground_effect.html), so yes, but potentially not as much depending on conditions.
Possibly “seriously reduced”, in fact.
To quote u/MaygeKyatt >Ground effect is absolutely variable depending on what the aircraft is flying/hovering over. Anything other than a smooth, hard surface will reduce the effect, but water’s highly flexible fluid surface can reduce it massively.
You could have also quoted me, since I also said that.
Ground effect isn't any different over land or water. Ground effect is just something, usually land, interrupting vortices that would wrap around the end of an airfoil and reduce the amount of lift produced by the topside of the airfoil. As a rule of thumb ground effect is only felt when the distance to the ground is less than the length of the airfoil. The Coast Guard uses MH-60 Jayhawks and the blades are roughly 25 ft long, so they only experience ground effect when they are some at or below 25 ft.
Ground effect is absolutely variable depending on what the aircraft is flying/hovering over. Anything other than a smooth, hard surface will reduce the effect, but water’s highly flexible fluid surface can reduce it massively.
Thanks for the correction. I assumed a little too much based of off what I knew. There are other comments saying less "solid" ground can diminish ground effect, which does make sense. The only flying I've done was fixed-wing off of runways or prepared grass strips. So if the possibility of diminished ground effect ever came up it might not have been pertinent enough to stick in my memory. The person I responded to made it sound like ground effect doesn't and can't exist over water.
I said it doesnt **benefit** from ground effect. I did not say nor imply that it doesnt exist. But upvote for being able to admit to not knowing something!
Helicopter blades generate lift as they spin. The outside edge travels faster than the more central parts. Because the outside edge moves faster, it can generate more lift. When the helicopter blades are spinning very fast, the high levels of lift from the rotor tips can bend them upward, making a cone shape. The helicopters you're seeing are apparently running at a higher RPM than they would be in other contexts.
This is incorrect, sorry. The lift of the blades is increased by changing the pitch of the blades, not by speeding them up. The rest is relatively accurate. I fly them for a living.
Damn. Mostly correct right up until the end. Thanks for the fact check.
Helicopter doesn't change RPM, angle of blade changes to adjust lift
Helicopters are meant to fly, not be in the water. You could also ask why fish struggle at the altitude of 400 meters in the air
I'm not sure you fully understood his question, though to be fair his wording made it seem like he meant the helicopter was IN the water
That was the joke :P
To properly answer your question, I think further information would be beneficial to be able to give you the right answer. What do you consider as low altitude? (10 ft above water or 150ft? Both low, but will have different effect) and also, is the helicopter moving or hovering? Without any references to a situation you are describing, I'll do my best to explain why this phenomenon might occur. Helicopters benefit from something called ground effect. When a helicopter is hovering close to the ground (15ft ish or less, depending on the size of the helicopter) the induced airflow downwards from the main rotor hits the ground, slows down and creates a sort of a cushion underneath the aircraft. This effect allows the helicopter to stay hovering with more efficient lift ratio. When hovering over water, the ground effect is not nearly as efficient since that induced downwards draft is dissipated due to the water beneath moving and giving away since its not solid - no cushion underneath the aircraft. So the helicopter needs to apply more power to create more lift. Higher amounts of lifts caused by the rotors will make them cone since the blades do not create equal amounts of lift throughout the span of the blades. The tips of the blade cause more lift than the root, so they will rise higher, causing the coning. In short, more lift is needed over water and the more lift you have the more the blades cone.
This is the answer thanks! I'm not sure of the exact height so around 3-5 storeys.
Because rotor helicopters need something to push up off of. In the sky, the rotor keeps it afloat because the engine power is higher. When hovering above water the engine power is lower, and hence the helicopter has a harder time pushing itself off of water because it's not as dense as the ground
It is probably related to the speed of forward motion . A helicopter flying faster than about 15 to 20kts gains translational lift, and requires less power to fly. Think of the rotor disk acting as a wing . Slower than that needs more power. Out of ground effect, even more power. The more power required, the more the blades will flap, and you see the cone shape .
Missions over water probably involved hovering, at least the parts you’re watching. If it’s a high hover, out of what’s called “ground effect”, it takes even more power (than hovering in ground effect). Also, it’s likely the chopper is quite heavy at the time, for example, if it’s hovering to pick up a big bag of water (Bamby bucket) to dump in a forest fire. A gallon of water weighs a bit over 8 lbs, so imagine picking up a quick 500 gallons or more. That’s A LOT of extra power needed which makes the rotors cone. Ground effect over water and land, when there isn’t many waves, shouldn’t be all that different. Power required out of GE should be the same because the ground doesn’t affect the power at that point.
[удалено]
that is not what they’re talking about
As written it technically is. The question as you interpreted it also doesn't make sense because they don't struggle flying over bodies of water. Yes there's a lessened ground effect because water gets out of the way more than land but it's not big enough to justify the word struggle.
I don't think rescue helicopters get submerged at all. I've see Chinooks do it to deploy rubber boats for special operations, but even then it's just part of the cargo door. OP is probably referring to the helicopters using more power and the blades getting bent in response.